Mars at Opposition 2018: How to See It and What to Expect

Get ready to see the Red Planet up close this week: Just after Mars reaches opposition with the sun July 27, 2018, observers on Earth will have their closest view of the planet since 2003.

Mars and Earth both orbit the sun, but at different distances, and thus, different speeds. Every two years or so, Mars, Earth and the sun form a straight line during the course of their orbits, with Earth in the middle — an event known as opposition.

Mars arrives at opposition on the same day as July's full moon. For some lucky skywatchers, that means they also have the chance to see a total lunar eclipse. That eclipse, which will not be visible from the United States, will be the longest lunar eclipse of the 21st century. You can see our full guide for that event here: Blood Moon 2018: Longest Total Lunar Eclipse of Century Occurs July 27

Closest since 2003

Mars reaches opposition, as in this artist's illustration, when it's opposite from the sun in Earth's sky.

Credit: NASA

During the Mars opposition in 2003, the Red Planet was only 34.6 million miles (55.8 million kilometers) from Earth. This was the closest the two planets had come to each other in almost 60,000 years, and this record won't be broken until Aug. 28, 2287, according to NASA.

Leading up to this year's opposition in July, Mars will continue to brighten in our sky. By June 26, Mars will be just 44 million miles (70.8 million km) away, and from the perspective of skywatchers on Earth, it will appear five times brighter than usual. By the time the Red Planet reaches its closest point to Earth, it will be a mere 35.8 million miles (57.6 million km) away and will have nearly doubled in brightness since June 26. [8 Cool Destinations That Future Mars Tourists Could Explore]

What, exactly, is an opposition?

Mars orbits the sun at a greater distance than Earth. As the distances increase, the orbital period also increases, so Mars takes about two Earth years to complete one orbit around the sun. Due to these different orbital speeds, every two years or so, Earth passes between Mars and the sun. This means that Mars and the sun are on directly opposite sides of Earth.

However, since both planets have elliptical orbits, some Earth-Mars encounters are closer than others. In July, Mars will be closer to Earth than it has been since 2003, though the Red Planet's next-closet approach won't occur until 2035.

In addition, this year, Mars will reach what is called "perihelic opposition". Perihelion refers to the point in Mars' orbit when it's closest to the sun. Therefore, when Mars is closest to the sun, it is even closer to Earth during opposition.

Throughout May, both Mars and Saturn were visible, and the best views will be in the predawn hours of the Northern Hemisphere. Mars was easily distinguished by its reddish color, while Saturn appeared golden. Mars moved east of Saturn by mid-May, into the constellation Capricornus, according to EarthSky.org.

But don't be fooled — while Mars will shine big and brightly leading up to and during opposition, the Red Planet is only about half the size of Earth. This means that even at its closest approach this summer, it will only be 24.3 arc seconds across when viewed from Earth. In comparison, the angular diameter of the moon is 1,800 arc seconds, which is about 75 times larger.

Editor's note: If you snap an amazing photo of Mars and would like to share it with Space.com for a story or photo gallery, send comments and images to spacephotos@space.com.

Samantha Mathewson joined Space.com as an intern in the summer of 2016. She received a B.A. in Journalism and Environmental Science at the University of New Haven, in Connecticut. Previously, her work has been published in Nature World News. When not writing or reading about science, Samantha enjoys traveling to new places and taking photos! You can follow her on Twitter @Sam_Ashley13.